Apparatus for applying heat-sealed seams to at least two-ply composite material of which the confronting plies

ABSTRACT

The invention relates to an apparatus for applying heat-sealed seams to at least two-ply composite material of which the confronting plies are heat-sealable at the operating temperature and the plies facing heat-sealing jaws are adapted to transmit the sealing heat without changing their structure. Such material is primarily used in machines for making hermetically sealed bags so that the humidity and aroma of the contents remain unaffected by the atmosphere. The inner ply of the bag can be a thermoplastic material while the ply which later forms the outside of the bag is either a non-thermoplastic carrier material such as aluminum foil or paper or a plastics material which has a higher melting point than the inner ply.

United States Patent [191 Bosse 1March 20, 1973 [75] Inventor: FrankBosse, Am Wasserwerk, Germany [73] Assignee: Winrlmoller & Holscher,

Westphalia, Germany [22] Filed: Feb. 2, 1971 [21] Appl. No.: 111,842

[52] US. Cl. ..156/583, 100/93 P [51] Int. Cl. ..B30b 15/34, B02c 1 1/08[58] Field of Search ..l56/583; 100/93 P [56] References Cited UNITEDSTATES PATENTS 2,802,086 8/1957 Fener ..l56/583 3,624,836 11/1971 Rohdin..156/583 3,198,685 8/1965 Kopito et al ..'....l56/583 PrimaryExaminer-Douglas J. Drummond Attorney-Fleit, Gipple & Jacobson [5 7]ABSTRACT The invention relates to an apparatus for applying heat-sealedseams to at least two-ply composite material of which the confrontingplies are heat-sealable at the operating temperature and the pliesfacing heat-sealing jaws are adapted to transmit the sealing heatwithout changing their structure. Such material is primarily used inmachines for making hermetically sealed bags so that the humidity andaroma of the contents remain unaffected by the atmosphere. The inner plyof the bag can be a thermoplastic material while the ply which laterforms the outside of the bag is either a non-thermoplastic carriermaterial such as aluminum foil or paper or a plastics material which hasa higher melting point than the inner ply.

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APPARATUS FOR APPLYING HEAT-SEALED SEAMS TO AT LEAST TWO-PLY COMPOSITEMATERIAL OF WHICH THE CONFRONTING PLIES For the purpose of applyingheat-sealed seams either transversely to or lengthwise of the directionin which the composite material runs through the bag-making machine,sealing jaws are used for engaging between each other the compositematerial which has been folded to double thickness, at least one of thejaws being electrically heatable.

in one form of heat-sealing apparatus, only one of the jaws is heatedand is in the form of an aluminium rail. The other jaw is unheated andprovided with an elastic layer of silicon rubber. The elastic layer to alarge extent compensates for differences in the thickness of thematerial to be heat-sealed lengthwise of the intended seam, suchdifferences occurring, for example, if the seam runs through preformedside folds for the bags to be made from the material. The elastic layeron the unheated jaw of the heat-sealing apparatus therefore ensures thata reasonably uniform pressure is exerted on the material to beheat-sealed. However, the apparatus has the disadvantage that thesealing heat is transmitted from only one side of the compositematerial, namely, firstly through the carrier material to the first plythat is to be heat-sealed and through this ply to the confronting secondply. The two plies to be heat-sealed are therefore heated unevenly andit is impossible to produce a good seam, especially for thickermaterials and if the number ofplies is different.

To avoid this disadvantage, it is possible also to heat the jaw providedwith the silicon rubber layer so that the plies to be heat-sealed willbe heated from both sides. This will result in a relatively goodheat-sealed seam but accurate temperature control is difficult becausethe heat from one jaw has to pass through the elastic layer. Thedifficulty of temperature control at the jaw having the elastic layerthereforemakes it impossible to use such an apparatus for heat-sealingcomposite materials consisting of a plastics carrier film such aspolypropylene and a plastics inner ply such as polyethylene if themelting point of the carrier film is only slightly higher than that ofthe inner ply. However, since such materials often have to beheat-sealed and since accurate temperature control at the sealing jawsis important, it has been necessary to dispense with an elastic layeraltogether. Consequently, if the sealing bars of the jaws are even onlyslightly inclinedas will occur with differences in the thickness of thecarrier material, the inner ply to be heat-sealed will be squeezed off.

Another disadvantage associated with known'heatsealing equipment is theapplication of pressure by means of two or more pressers which transmitthe pressure to the sealing bar of one of the jaws at isolated points,therebyv preventing the formation of seams having substantially the samequality throughout their lengths.

The invention aims to provide heat-sealing apparatus which permitsdifferences in the thickness of the composite material to becompensated, the temperature to be controlled as accurately as possibleand seams to be formed which are of substantially the same good qualitythroughout their entire length.

According to the invention, apparatus having sealing jaws forheat-sealing two or multi-ply compositematerial in which the confrontingplies are heat-sealable at the operating temperature and the pliesfacing the jaws are adapted to transmit the sealing heat withoutchanging their structure comprises an elastic layer for one of the jawsto compensate for differences in the thickness of the composite materialalong the intended heat seal, the elastic layer being disposed between aheated flexible sealing bar and support means for the sealing bar. Thus,the elastic layer is provided on the side of the sealing bar remote fromthe composite material to be heat-sealed so that the heat need no longerpass through the rubber layer but will be transmitted direct to thecomposite material. By reason of the low section modulus, that is to saythe low resistance to bending of the sealing bar which is kept as flatas possible, the sealing bar can simply flex and adapt itself topossible differences in thickness of the composite material, suchflexure of the sealing bar being compensated by the elastic layerinterposed between the sealing bar and the rigid support means for thesealing bar.

To avoid excessive transmission of heat from the sealing bar to otherparts of the apparatus, the support means forthe sealing bar maycomprise a base bar, a thermally insulating intermediate layer and anintermediate bar, the intermediate bar being disposed adjacent thesilicon rubber or other elastic layer and the sealing bar. Theflexibility of the sealing bar along its entire length can befacilitated if it comprises a portion having a cross-section whichconverges towards its heating surface, the sealing bar being held to itssupport means by metal sheathing which is fixed to the support means andembraces the converging portion of the sealing bar so that the heatingsurface projects the beyond the sheathing. In this way the sealing baris mounted so that it can be freely displaced towards the elastic layerfor the purpose of compensating unevenness in the plies to beheat-sealed. Further, it is of advantage for each end of the sheathingto comprise a tab which engages around the ends of the sealing bar. Thetabs are preferably resilient to allow for elongation of the sealing barcaused by expansion under heat.

In one form of the invention, the sheathing is provided with a thermallyinsulating lining which is preferably of asbestos. These asbestos layersextend along the longitudinal sides of the sealing bar and, togetherwith the aforementioned thermally insulating intermediate layer disposedbetween the base bar and the intermediate bar, define a thermallyinsulating shell which surrounds the sealing bar and the elastic layerand 'ensures that almost all the available heat is transmitted to theoperative or heating surface of the sealing bar. The thermallyinsulating shell has the particular purpose of avoiding heat radiationfrom. the elastically mounted sealing bar, heat rising beyond the regionof the searn'alsobeing kept to a minimum and possible overheating of thematerials beyond the region of the seam beingprevented. The intermediatebar beneath the silicon rubber layer serves as a so-called heat cushionwhich substantially equalizes fluctuations in the temperature control.In addition, relatively rapid heating of the sealing bar is possibleafter the apparatus has been switched off for a short time.

A heating element for the sealing bar is preferably of rod form and caneither be embedded in the sealing bar by moulding or casting it therein,thereby excluding any air pockets that might have an insulating effect,or it can be inserted in a groove of the sealing bar and covered by aplate which is an accurate fit in the groove and which may be pinned tothe sealing bar.

To prevent the carrier or outer ply of the composite material from beingbaked onto the heated sealing bar, the heating surface of the latter ispreferably covered by a non-stick film such as polytetrafluoroethylenewhich is wound on rotatable shafts along each side of the sealing jaw,provision being made intermittently to lock the shafts against rotation.

The jaw carrying the elastic layer may be the lower jaw fixed to a frameof the apparatus whilst the other jaw is movable by a plurality ofhydraulic or pneumatic pistons having piston rods which, by means ofpivot pins extending transversely to the length of the jaws, are hingedto pressers for supporting members for the said other jaw extendinglongitudinally thereof. The hinged mounting of the pressers for thesupporting members ensures that the other jaw, which is not providedwith an elastic layer, can also freely adapt to any irregularities inthe composite material to be heatsealed. In addition, the supportingmembers extending longitudinally of the jaw avoid application of thepressure to the jaw at isolated points and consequent bending thereof.One of the supporting members is preferably held to its associatedpresser against displacement, for example by a pin on the supportingmember engaging in a recess of the presser, whilst the other supportingmembers are slidable with respect to their pressers lengthwise of thejaw so as to avoid difficulties that might otherwise arise by variationsin length caused by heating of the jaw. If, as is preferred, the upperjaw of the apparatus is movable, the supporting members can be held ingrooves of the pressers by tension springs, this enabling easydismantling of the jaw and again making allowance for thermal elongationwhich precludes rigid mounting of the supporting members to thepressers. The pressers associated with the outer supporting members maybe provided with guide grooves for the respective supporting memberswhilst the inner presser or pressers have no guide grooves and thusexclusively serve to transmit the pressure and prevent difficulties inguiding. To minimize the amount of heat transmission from the movablejaw, the side of the supporting members facing the jaw may be pro- 5vided with channels which extend transversely of the jaw, the channelsdefining ribs through which only a relatively small amount of heat canbe transmitted.

The movable jaw and means for moving same may be mounted on a pivotablebeam to facilitate adjustment and maintenance of the apparatus.

Examples of the invention are illustrated in the accompanying drawingswherein:

FIG. 1 is a fragmentary plan of a heat-sealing apparatus;

FIG. 2 is an enlarged section on the line IlII in FIG.

FIG. 3 is an enlarged section on the line III-III of FIG. 1 but showinga modification of the way in which a heating element is mounted in asealing bar;

FIG. 4 is a section on the line lV-IV in FIG. 1;

FIG. 5 is a section on the line V-V in FIG. 1, and

FIG. 6 is a view taken in the direction of the arrow B in FIG. 5.

The heat-sealing apparatus illustrated in FIG. 1 comprises a sealing jaw2 fixed to a table 1 of the apparatus. The jaw 2 co-operates with asealing jaw 4 which is movable in the direction of the arrows 3 to applypressure to composite material which is to be heat-sealed between thejaws. The lower portion of the jaw 2 corn prises a base bar 5 providedwith lugs 8 and 9 having holes 6 and .7 (also see FIG. 3). For thepurpose of fixing the base bar 5, the table 1 is provided with T-shapedchannels 10 and 11 containing T-shaped nuts 12 and 13 engaging bolts 14and 15 passed through the holes 6 and 7. To adjust the jaw 2 in thedirection of the arrow 16 shown in FIGS. 2 and 3, the bolts 14 and 15are loosened and the jaw 2 is displaced so that the bolts 14 and 15 andthe nuts 12 and 13 can slide along the channels l0 and 11. The jaw 2 isfixed in position after adjustment by tightening the bolts 14 and 15. Tominimize the heat transmitting surface between the jaw 2 and the table1, the base bar 5 is provided with transverse holes 17 at uniformintervals along its length. Provided on the base bar 5 there is anasbestos intermediate layer 18 which is covered by an intermediate bar19. To fix the intermediate bar 19 to the base bar 5, the latter isprovided with countersunk holes 20 at uniform intervals along its lengthto align with corresponding holes 21 in the asbestos layer 18. Bolts 22are passed through the aligned holes 20 and 21 and engaged in tappedholes 23 of the intermediate bar 19. The components which are thusbolted together, namely the base bar 5, the intermediate asbestos layer18 and the intermediate bar 19, together form support means for aheat-sealing bar 25, an elastic layer 24 of, say, silicon rubber beinginterposed between the support means and the sealing bar 25. A lowerportion 25 of the sealing bar 25 is of parallelepiped form (FIG. 3) andhas a width corresponding to the width of the intermediate bar 19 andthe elastic layer 24. In the vicinity of the operative or heatingsurface 26 of the sealing bar (FIGS. 2 and 3), the latter has a portion25" of which the crosssection converges trapezoidally towards aparallelepiped portion 25" which defines the actual heating surface 26.The sealing bar 25 is as flat as possible so that its resistance tobending is sufficiently small for the bar to adapt itself to anyirregularities in the composite material to be heat-sealed and therebypermit substantially uniform heat-sealing along the entire 0 length ofthe bar 25.

A heating element 27 of rod form is provided within the sealing bar 25.In the FIG. 2 embodiment, the heating element is cast or moulded intothe bar 25 whilst in FIG. 3 the element 27 is an accurate fit in agroove 28 of the sealing bar and fully covered by an accurately fittingplate 29. The cover plate 29 is fixed to the bar 25 by means ofuniformly spaced pins 30 (FIGS. 1 and 3).

The two longer sides of the intermediate bar 19 (FIG. 3) and the sealingbar 25 are covered with asbestos layers 31 and 32 which are fixed tometal sheathing 35 and 36 and to the intermediate bar 19 by means ofbolts 33 and 34. The asbestos layers 31 and 32 and the sheathing 35 and36 extend from the asbestos intermediate layer 18 up to the taperedfaces of the converging portion 25" of the sealing bar and are benttherearound to hold the sealing bar 25 to the elastic layer 24. In orderthat the sheathing 35 and 36 will not project beyond the side faces ofthe base bar 5, the width of the base bar 5 and of the intermediatelayer 18 is larger than that of the intermediate bar 19, elastic layer24 and sealing bar 25 by an amount equivalent to the thickness of thelayers 31 and 32 and sheathing 35 and 36. The ends of the sheathing 35and 36 are provided with tabs 37, 37' and 38, 38 (FIGS. 1 and 2), everytwo of which lie against the associated end face of the sealing bar 25.The tabs 37, 37' and 38, 38 are preferably resilient so that, whilstthey will hold the sealing bar 25 against longitudinal displacement,they will yield to elongation of the bar 25 caused by heating.

To prevent the composite material that is to be heatsealed from bakingonto the sealing bar 25, the heating surface 26 of the latter isprovided with a silk cover 39 (FIG. 3) which is coated or impregnatedwith polytetrafluoroethylene and which is wound onto winding shafts 43and 44 that are mounted on both sides of the jaw 2 in bearings 41 and 42secured to the ends of the intermediate bar 19 by bolts 40. Each of thewinding shafts 43 and 44 consists of two bars 45, 46 and 47, 48 (FIG. 3)which are of rectangular cross-section, are interconnected by bolts 43and 44' and between which the polytetrafluoroethylene film 39 isclamped, the film having appropriate holes for the bolts 43' and 44'.One bar 46 or 48 of each shaft 43 or 44 is provided at its ends withtrunnions which engage in the bearings 41 and 42 and the ends of whichare provided with a screwthread 49 and 50 for engaging a nut 51 and 52(FIGS. 1 and 2). After the tension of the protecting film has been set,the nuts 51 and 52 can be tightened against the bearings 41 and 42 sothat the shafts 43 and 44 are locked against rotation.

The upper jaw 4 (FIGS. 1 and 4) which is movable in the direction of thearrows 3 and exerts pressure during heat sealing is similarly equippedwith a protecting film. A heating element 53 of rod form is sealed intothe jaw 4, one end 54 of the heating element projecting from the jaw forconnection to an electric terminal. For the same purpose,'one end 55(FIG. 1) of the heating element 27 in the sealing bar 25 also projectsfrom the jaw 2. The two ends of a heatingcoil within each heatingelement 27 and 53 pass through theprojecting ends'54 and 55 to atransformer (not shown).

Reciprocating movement of the sealing jaw 4 in the direction of thearrows3 and transmission of the pressure during heat sealing is effectedby three spindles 56 which are actuated and controlled by hydraulic orpneumatic pistons located in cylinders '57. The cylinders 57 are mountedon a web 58 (FIGS. 1 and 4) of a U-section bridge '59 and fixed theretoby screwthreads 60. The ends of the limbs Hand 62 of the U-sectionbridge rest on columns 65'and 66-which are fixed to the table 1 by bolts63 and 64 (FIG. 1). The bolts 63 and 64 are passed through T-channels 67and 68 in'the table '1 and can slide in the channels for the purpose ofadjusting the bridge'59 and the sealing jaw 4 carried thereby in thedirection'of the arrows '16 (FIG. 4). The end of the column 65 remotefrom the table 1 is providedwith a sleeve 69 which engages a pivot pin70 of which both ends project from the sleeve and engage in holes in thelimbs 61 and 62 of the bridge so that the bridge can be swung about thepivot pin 70. To lock the bridge 59 in a predetermined angular position,the limbs 61 and 62 lie in corresponding recesses 71 and 72 (FIG. 5) atthe top of the column 66. Between the recesses 71 and 72 there is afurther recess 73 for receiving one end of a leverlike bolt 74. A hingepin 76 in a hole at the top of the column 66 in the region of the recess73 also passes through a hole 77 in the end of the lever-like bolt 74,the bolt 74 being pivotable about the hinge pin 76. The bolt 74 can beswung up to a slot 78 in the web 58 of the bridge 59 (FIGS. 5 and 6),the screw-threaded end projecting beyond the web 58. This end of thebolt 74 is provided with a washer 79 and a nut 80 by which the bridge 59can be fixed in the predetermined position. However, the aforementionedbridge construction and its displaceability are mentioned strictly byway of example. In another construction, the bridge may be a fixed frameequipped with rails which replace the web 58 and in which the individualcylinders 57 are longitudinally displaceable and fixable with the aid ofan elongated hole.

The following is a description of one of three identical suspensions forthe upper sealing jaw 4. The spindle 56 reciprocatable in the directionof the arrows 3 in FIGS. 1 and 4 is provided with a screwthread 81 atthe end adjacent the jaw 4. The screwthread 81 is engaged in a firstelement 82 of a hinge 83. To clamp the spindle 56 tight, a clamping ring84 is fixed to the top of the element 82. The element 82 is embraced bya forked second element or presser 85 which can swing about a pivot pin86 extending transversely to the jaw 4 and interconnecting both elements82 and 85. The pressers 85 nearest the ends of the jaw 4 are eachprovided with a groove 87 which receives a steel plate 88 having thesame width as the jaw 4. To avoid an excessively rigid connection, thepressure face of thecentral presser 85 is plain and therefore thecentral presser merely transmits pressure to the associated steel plate88.

The plates 88 constitute supporting members for the jaw 4. Each suchplate is screwed .to the jaw 4 by bolts 90 and 91, an interposed metalplate 89 serving as a shim. The length of the plates 89 and 88 is suchthat they cover an adequately large part of the rear face of the jaw 4and distribute the pressure to be exerted thereon. One end of the plate89 is flanged upwardly at 92-and connected to one end of a tensionspring 93 of which the other end'is fixed to a pin 94 anchored in thehinge element 82. The spring 93 pulls the jaw 4 into engagement with thepresser 85 To minimize the transmission of heat from the jaw 4 totheremainder of the apparatus, the face of the plate 88 adjacent .thejaw 4 is provided with grooves 95 which extend transversely to thelength of the jaw 4.

The ribs 96'left between adjacent grooves in covoperavtion with theplate89. ensure that thesurface of the jaw 4 is substantially uniformlyloaded.

Elongation of the jaw 4 is taken into account by providing thatonlyoneouter presser 85 is-provided withapin 97 which projects from the,groove 87 and engages-ina hole in the plate 88. .When the jaw 4elongates under thermal effects, the plate 88 at the other endoftheapparatuscan slide in thegroove 87.0f the presserwhich is here notprovided with a pin equivalent to the.pin-97, whilst in the centralregion of .the apparatus the plate 88 is in any case not guided in thepresser 85.

Adaptation of the pressers to the sealing jaw 4 takes place by turningthe screw-threaded spindles- 56, this being effected by a transversehole 98 at the upper projecting end of each spindle 56.

I claim:

1. Apparatus having sealing jaws each of said sealing jaws beingequipped with a flexible sealing bar, each of the said sealing barsbeing heated by a heating element of rod form, said heating elementsbeing inserted into the pertaining sealing bar, the apparatus comprisingan elastic layer to compensate for differences in the thickness of theplies of material to be sealed between the sealing jaws along theintended heat seal, the elastic layer being disposed between the sealingbar of one of said sealing jaws and support means for that sealing bar.

2. Apparatus according to claim 1 wherein the jaw carrying the elasticlayer is fixed to a frame and the other jaw is movable by a plurality ofhydraulic or pneumatic pistons having piston rods which, by means ofpivot pins extend transversely to the length of the jaws, are hinged tosupporting members for the said other jaw extending longitudinallythereof.

3. Apparatus according to claim 1, wherein the said support meanscomprise a base bar, a thermally insulating intermediate layer and anintennediate bar.

4. Apparatus according to claim 1, wherein the sealing bar comprises aportion having a cross-section which converges towards its sealingsurface and the sealing bar is held to its support means by metalsheathing fixed to the support means, the sheathing embracing theconverging portion of the sealing bar so that the heating surfaceprojects beyond the sheathing.

5. Apparatus according to claim 4, wherein each end of the sheathingcomprises a tab engaging around the ends of the sealing bar.

6. Apparatus according to claim 5, wherein the tabs are resilient.

7. Apparatus according to claim 4, wherein the sheathing is providedwith a thermally insulating lining.

8. Apparatus according to claim 1, wherein said heating element of rodform is moulded into the sealing bar.

9. Apparatus according to claim 1, wherein said a heating element of rodform is inserted in a groove of the sealing bar and covered by anaccurately fitting plate.

10. Apparatus according to claim 1, wherein the heating surface of thesealing bar is covered by a nonstick film wound on rotatable shaftsalong each side of said one jaw.

11. Apparatus according to claim 10, wherein the non-stick filmcomprises polytetrafluoroethylene.

12. Apparatus according to claim 5, wherein the supporting members areassociated with pressers, one of the supporting members being held toits associated presser against displacement whilst the others areslidable with respect to their pressers lengthwise of the jaws.

13. Apparatus according to claim 12, wherein the supporting members areheld to the pressers by tension springs.

14. Apparatus according to claim 12, wherein there are at least threesupporting members for the said other jaw, the pressers associated withthe outer supporting members being provided with guide grooves for theUNITED STATES PATENT OFFICE CERTIFICATE OF. CORRECTION Patent No. .7 1.0 I Dated March 20; 1973 Iriventor(s) FRANK BOSSE It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

On the titlepage, insert the following:

- [30] Foreign Application Priority Data Signed and sealed this 9th dayof April 197E.

(SEAL) Attest:

EDWARD M.FU1ITCHEH,JR. C. MARSHALL DAMN Attesting Officer Commissionerof Patents FORM PC3-1 uscoMM-Dc 6O376-P69 U45. GOVERNMENT PRINTINGOFFICE: 1969 0-366-334

1. Apparatus having sealing jaws each of said sealing jaws beingequipped with a flexible sealing bar, each of the said sealing barsbeing heated by a heating element of rod form, said heating elementsbeing inserted into the pertaining sealing bar, the apparatus comprisingan elastic layer to compensate for differences in the thickness of theplies of material to be sealed between the sealing jaws along theintended heat seal, the elastic layer being disposed between the sealingbar of one of said sealing jaws and support means for that sealing bar.2. Apparatus according to claim 1 wherein the jaw carrying the elasticlayer is fixed to a frame and the other jaw is movable by a plurality ofhydraulic or pneumatic pistons having piston rods which, by means ofpivot pins extend transversely to the length of the jaws, are hinged tosupporting members for the said other jaw extending longitudinallythereof.
 3. Apparatus according to claim 1, wherein the said supportmeans comprise a base bar, a thermally insulating intermediate layer andan intermediate bar.
 4. Apparatus according to claim 1, wherein thesealing bar comprises a portion having a cross-section which convergestowards its sealing surface and the sealing bar is held to its supportmeans by metal sheathing fixed to the support means, the sheathingembracing the converging portion of the sealing bar so that the heatingsurface projects beyond the sheathing.
 5. Apparatus according to claim4, wherein each end of the sheathing comprises a tab engaging around theends of the sealing bar.
 6. Apparatus according to claim 5, wherein thetabs are resilient.
 7. Apparatus according to claim 4, wherein thesheathing is provided with a thermally insulating lining.
 8. Apparatusaccording to claim 1, wherein said heating element of rod form ismoulded into the sealing bar.
 9. Apparatus according to claim 1, whereinsaid a heating element of rod form is inserted in a groove of thesealing bar and covered by an accurately fitting plate.
 10. ApparatusaccordinG to claim 1, wherein the heating surface of the sealing bar iscovered by a non-stick film wound on rotatable shafts along each side ofsaid one jaw.
 11. Apparatus according to claim 10, wherein the non-stickfilm comprises polytetrafluoroethylene.
 12. Apparatus according to claim5, wherein the supporting members are associated with pressers, one ofthe supporting members being held to its associated presser againstdisplacement whilst the others are slidable with respect to theirpressers lengthwise of the jaws.
 13. Apparatus according to claim 12,wherein the supporting members are held to the pressers by tensionsprings.
 14. Apparatus according to claim 12, wherein there are at leastthree supporting members for the said other jaw, the pressers associatedwith the outer supporting members being provided with guide grooves forthe respective supporting members.
 15. Apparatus according to claim 5,wherein the supporting members are provided with ribs which extendtransversely of the jaws and lie against the said other jaw. 16.Apparatus according to claim 5, wherein the said other jaw and means formoving same are mounted on a pivotable beam.